Organic light-emitting diodes, or OLEDs, are examples of solid-state optoelectronic devices that can have several layers of organic material and polymers. An OLED device commonly includes a substrate, an anode, a hole-transporting layer made of an organic compound, an organic luminescent layer with suitable dopants, an organic electron-transporting layer, and a cathode. OLED devices are attractive because of their low driving voltage, high luminance, wide-angle viewing and capability for full-color flat emission displays.
Optoelectronic devices, especially OLEDs, are generally prone to degradation under ambient environment conditions. For example, a common problem with OLED displays is sensitivity to moisture. Specifically, water vapor in the presence of oxygen may cause undesired crystallization and formation of organic solids within the device; undesired reactions at the electrode-organic layer interfaces; corrosion of metals and the undesired migration of ionic species; and the like. The water related degradation often manifests itself as the growth of dark spots in the emissive areas of the OLED, which can lead to performance loss, operational instability, poor color and emission accuracies, and shortened operational life. Dark spot growth in quantity, size and location is usually based upon the time and extent of exposure to degrading conditions.
To minimize such degradation mechanisms, optoelectronic devices such as the organic light-emitting devices are typically encapsulated and hermetically sealed with barrier material. However, it is not easy to completely eliminate conditions that may degrade an electronic device. Encapsulation methods themselves may trap some residual moisture within the device. Furthermore, even in an encapsulated environment, it is difficult to prevent all degradation, which inevitably occurs over time.
Thin film encapsulation is advantageous over the use of glass or metal caps with epoxy sealants and desiccants because it is more cost effective with a simpler process. However, throughput is generally limited. Currently, the tact time (time required to complete a fully encapsulated OLED) for thin film encapsulation of opto-electronic devices is longer than what is required for a commercially viable process. To increase throughput, manufacturers tend to utilize multiple plasma deposition reactors, which is not cost effective and consumes a significant footprint.
Accordingly, there exists a need for improved methods for encapsulation of optoelectronic devices so as to improve tact time, throughput and productivity